A heel holder of the above-mentioned type is for example described in U.S. Pat. No. 3,776,567. In this known design the upper end of the abutment which closes off the spring chamber is threadedly engaged with a rod coaxially extending through the center of the spring, the lower end of which rod extends through the bottom of the spring chamber and is swingably supported on a pin fixed to the bearing block. Control cam surfaces are provided which are arranged on the edges of the two sidewalls of the bearing block facing the sole down-holding means. Each control cam surface has a region which extends vertically with respect to the upper side of the ski and a curved region, the center of curvature of which lies on the axis of the aforesaid pin. The sole down-holding means is adjustable on the housing in elevational direction and is therefore designed as a separate structural part. The spring chamber and thus also the spring are arranged vertically in the downhill skiing position of the heel holder. However, the spring force acts through the sole down-holding means onto the heel of a ski shoe inserted into the binding to press only in the vertical direction onto the ski shoe, thus toward the upper side of the ski. Thus, it is necessary to hold and prevent the heel of the ski shoe from moving laterally which is done by means of a further structural part which has two lateral sole holders and is also swingably supported. The desired effect mentioned in this reference is that no force whatsoever is to be applied from the heel holder onto the front jaw. However, this in practice results in undesired disadvantages. For example, this binding is not capable of compensating for a bending of the ski, as it occurs for example during skiing on slopes with many moguls and results in a deformation of an inserted ski shoe or also in an insufficient holding of the inserted ski shoe in the binding. Furthermore, it is disadvantageous in this heel holder that the control cam surfaces which are provided for determining a release operation are exposed thereby raising the risk that both dirt and ice will accumulate therein. Since the control bolt, functional during a release operation, is not forceably guided on the control cam surfaces, it can lift off from the control cam surfaces so that their function as "control cam surfaces" is jeopardized.
A further heel holder is described in Austrian Pat. No. 357 076 and in the corresponding U.S. Pat. No. 4,088,344. In this heel holder, a rotatably supported disk is held on each of the sidewalls of the bearing block. In each disk there is provided a control cam surface which is angled at an obtuse angle. The range of rotation of the disks is limited by stops. A control bolt is guided on the control cam surfaces, which control bolt is fixedly connected to a swingable housing. A spring is arranged in a spring chamber provided on the housing. One end of the spring is supported on a pin which extends through the spring chamber and which is anchored on the sidewalls of the bearing block. The initial tension of the spring cannot be changed. In order to adjust for different release forces, each cam is adjustable on both sides by means of a screw on a release lever hingedly secured to the bearing block. The cams determine the position of stops on the disks and thus the respective setting angle of the control cam surfaces, whereby a large setting angle causes a high release force. An important disadvantage of this conventional heel holder consists in it having many structural parts and an expensive release mechanism. Due to the many structural parts which are frictionally coupled, uncontrollable frictional forces develop. Thus it has been proven in practice that during successive releases very different and seldom reproducible release values occur, which raises the risk of injury to a skier using the binding.
Therefore, the purpose of the invention is to provide a heel holder of the above-mentioned type which does not have the disadvantage of conventional types of construction, which is easily constructed and assures also in extreme situations constant release values.
This set purpose is inventively attained by each control cam surface being constructed on the inside of the sidewall of the bearing block, by the pivot axis of the housing being arranged on the upper area of the bearing block, and by the pivot axis being offset rearwardly relative to the control bolt.
Thus the control cam surfaces are protected against outside influences. By positioning the pivot axis relative to the two control cam surfaces, the bolt which is held on the housing is pressed against the control cam surfaces to assure, on the one hand, a secure holding of a ski shoe inserted into the binding and, on the other hand, a proper and repeatable release function determined by the control cam surfaces in all situations.
An important concept of the invention consists in each control cam surface being formed by the edges of an arcuately shaped recess in each of the sidewalls of the bearing block, wherein each control cam surface has a first curved section, the tangent to which defines a starting portion which is oriented at an acute angle .alpha. greater than 12.degree., preferably at approximately 75.degree., to the longitudinal axis of the ski, viewed from the side of the ski, and the tangent to the end portion of the curved section defines with the longitudinal axis of the ski an angle .beta., which is greater than 90.degree., preferably approximately 140.degree., whereby the length of the curved section determines the elasticity range of the heel holder. The release characteristic is precisely determined through these measures. The form of the curved section determines the course of the force over the covered distance in a force-distance-diagram.
During the further course each control cam surface is designed inventively so that the first curved section is followed by a further curved section, to assure a slight relaxing of the spring, wherein the relaxation distance of the spring is determined by the difference between two distances, wherein S is the distance of a point on the curved section from the pivot axis of the housing farthest from the pivot axis and s is the distance of a termination point on the first curved section from the pivot axis. The spring is compressed by the amount of this difference during a stepping into the binding. Thus the stepping-in force can be precisely determined or fixed.
A further concept of the invention consists in the adjustable abutment of the spring being held in a sleeve which is open on one side, which sleeve is held by pins forming the pivot axis of the housing on the bearing block. The sleeve has two shoulders received in guide grooves which are oriented parallel with respect to the longitudinal extent of the sleeve on the housing. These measures assure a movability of the housing relative to the sleeve without using additional structural parts.
The invention relates furthermore to a heel holder for a safety ski binding having a cross-country plate which carries the bearing block thereon and which can be swung upwardly about an axis which extends transversely with respect to the longitudinal axis of the ski, wherein the housing carries at least one cam engageable by a bolt arranged on the release lever and which extends transversely with respect to the longitudinal axis of the ski. The bolt also effects an operation of a locking element for locking or unlocking of the cross-country plate on the ski. The housing can by means of the release lever be swung with the sole down-holding means in the simplest manner into the open position. It is particularly preferable that the release lever can simultaneously operate a locking mechanism which is arranged below the heel holder.
A further preferable development of the invention relates to the provision of a release lever having a slide member thereon. The slide member has a locking lever to cause the movement of locking noses on the slide member to move into and out of locking recesses provided on the sidewalls of the bearing block and against the force of a spring. Separate locking recesses are provided for fixing the release lever in its cross-country skiing position and in its downhill skiing position. Thus a secure fixing of the release lever both in the downhill skiing position and also in the cross-country skiing position is assured. The slide member is operated manually in the simplest manner.
The spring on the slide member is according to a further characteristic of the invention compactly housed and without interference by placing same in a cavity on the release lever provided between the locking lever and the slide member. The spring is supported at its one end on the slide member and at its other end on a web portion on the release lever.
A further important inventive characteristic consists in the provision of a control guideway being provided on the bearing block and extending in a direction toward the tail of the ski, which guideway merges into the locking recesses, whereby, viewed in a side view, the distance of successive points on the control guideway from the axis of the release lever increases continuously, which control guideways are movable along the slide member during a swinging of the release lever in a clockwise direction against the force of the spring on the release lever. During a swinging of the release lever in the clockwise direction for effecting an arbitrary opening of the heel holder, the spring is compressed in the slide member and effects an automatic return of the release lever into its initial position as soon as the binding opens. This measure contributes to the comfortable operation of the heel holder and prevents the risk of injury, which could occur when the binding is closed and the release lever springs backwardly.